1. Field of the Invention
The present invention relates to a reluctance motor. Particularly, it relates to a reluctance motor which has a self-excitation function so as to achieve highly efficient rotation.
2. Description of the Related Art
Reluctance motors are mounted as drive sources on various kinds of drive devices. Each of the reluctance motors has a problem that it is difficult to obtain large torque when the reluctance motor is of a type using only reluctance torque, in comparison with a motor (electric motor) of a type which is driven by use of magnet torque generated by permanent magnets embedded on the rotor side.
Particularly, when a motor is mounted on a hybrid electric vehicle or an electric vehicle requiring large torque, the motor often uses an IPM (Interior Permanent Magnet) structure in which permanent magnets such as neodymium magnets having strong magnetic force are embedded in a V-shape in a rotor so that both magnet torque and reluctance torque can be used effectively.
For example, there has been proposed that a reluctance motor may use a self-excitation function as disclosed in Sakutaro Nonaka, “Self-Excitation Type Single-Phase Synchronous Motor”, IEEJ Transactions Vol. 78 No. 842, November 1958, P. 18-26 to improve efficiency. It has been desired to improve characteristics such as torque in a reluctance motor which can be manufactured inexpensively as an on-vehicle motor.
In the self-excitation system disclosed in Sakutaro Nonaka, “Self-Excitation Type Single-Phase Synchronous Motor”, IEEJ Transactions Vol. 78 No. 842, November 1958, P. 18-26, magnetic fluxes having a higher frequency than the fundamental frequency of drive currents supplied to stator-side drive coils are interlinked with the rotor side to generate induced currents in self-excitation coils disposed on the rotor side. In the self-excitation system, the induced currents are half-wave rectified and then supplied (returned) to the self-excitation coils so that the self-excitation coils can also serve as electromagnet coils.
However, in the self-excitation function disclosed in Sakutaro Nonaka, “Self-Excitation Type Single-Phase Synchronous Motor”, IEEJ Transactions Vol. 78 No. 842, November 1958, P. 18-26, the self-excitation coils serve also as the electromagnet coils. Accordingly, magnetic interference takes place so that the induced currents cannot be generated efficiently but electromagnetic force generated thus is also weakened.
In addition, in the structure disclosed in Sakutaro Nonaka, “Self-Excitation Type Single-Phase Synchronous Motor”, IEEJ Transactions Vol. 78 No. 842, November 1958, P. 18-26, the self-excitation coils are disposed up to deep portions isolated from an outer surface of the rotor. High frequency components (spatial harmonic components) of the magnetic fluxes cannot reach (interlink with) the deep portions of the rotor but only very small induced currents can be generated in the self-excitation coils.
Incidentally, a self-excitation type motor has been proposed also in JP-A-10-271781. However, it has the same problem because induced currents cannot be generated efficiently in the same manner.
In addition, it has been proposed in JP-A-2010-22185 that high frequency currents are separately inputted to stator-side coils to generate excitation currents in rotor-side self-excitation coils. However, it is necessary to input excitation energy from the outside so that drive with high efficiency cannot be expected (lowering in the efficiency cannot be avoided).